Re: [PATCH 4/4] misc: Add power-efuse driver

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Thu, Feb 17, 2022 at 02:44:44AM -0800, Zev Weiss wrote:
> This driver provides a sysfs interface to access the on/off state and
> error flags of a regulator supplying a power output controlled by the
> system.
> 
> Signed-off-by: Zev Weiss <zev@bewilderbeest.net>
> ---
>  MAINTAINERS                |   5 +
>  drivers/misc/Kconfig       |  15 +++
>  drivers/misc/Makefile      |   1 +
>  drivers/misc/power-efuse.c | 221 +++++++++++++++++++++++++++++++++++++
>  4 files changed, 242 insertions(+)
>  create mode 100644 drivers/misc/power-efuse.c

You add sysfs files, yet have no Documentation/ABI/ entry updates
documenting what those sysfs files do?  Please fix.

> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index fca970a46e77..d1153a0389d2 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -7064,6 +7064,11 @@ S:	Orphan
>  W:	http://aeschi.ch.eu.org/efs/
>  F:	fs/efs/
>  
> +POWER EFUSE DRIVER
> +M:	Zev Weiss <zev@bewilderbeest.net>
> +S:	Maintained
> +F:	drivers/misc/power-efuse.c
> +
>  EHEA (IBM pSeries eHEA 10Gb ethernet adapter) DRIVER
>  M:	Douglas Miller <dougmill@linux.ibm.com>
>  L:	netdev@vger.kernel.org
> diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
> index 0f5a49fc7c9e..45fc3e8ad35d 100644
> --- a/drivers/misc/Kconfig
> +++ b/drivers/misc/Kconfig
> @@ -470,6 +470,21 @@ config HISI_HIKEY_USB
>  	  switching between the dual-role USB-C port and the USB-A host ports
>  	  using only one USB controller.
>  
> +config POWER_EFUSE
> +	tristate "Power efuse driver support"
> +	depends on OF && REGULATOR
> +	help
> +	  This driver supports a regulator device functioning as a
> +	  power efuse, with status bits and an on/off switch available
> +	  via sysfs.
> +
> +	  A typical use for this would be for an efuse controlling a
> +	  generic power output for supplying power to devices external
> +	  to the system running this driver (such as in the management
> +	  controller of a "smart" PDU or similar), allowing the
> +	  operator to manually turn the output on and off, check if
> +	  the efuse has tripped due to overload, etc.
> +
>  source "drivers/misc/c2port/Kconfig"
>  source "drivers/misc/eeprom/Kconfig"
>  source "drivers/misc/cb710/Kconfig"
> diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
> index a086197af544..7bd784b89ef8 100644
> --- a/drivers/misc/Makefile
> +++ b/drivers/misc/Makefile
> @@ -59,3 +59,4 @@ obj-$(CONFIG_UACCE)		+= uacce/
>  obj-$(CONFIG_XILINX_SDFEC)	+= xilinx_sdfec.o
>  obj-$(CONFIG_HISI_HIKEY_USB)	+= hisi_hikey_usb.o
>  obj-$(CONFIG_HI6421V600_IRQ)	+= hi6421v600-irq.o
> +obj-$(CONFIG_POWER_EFUSE)	+= power-efuse.o
> diff --git a/drivers/misc/power-efuse.c b/drivers/misc/power-efuse.c
> new file mode 100644
> index 000000000000..e974dde57615
> --- /dev/null
> +++ b/drivers/misc/power-efuse.c
> @@ -0,0 +1,221 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * This module provides a thin wrapper around a regulator device that exposes
> + * status bits and on/off state via sysfs.
> + *
> + * Copyright (C) 2022 Zev Weiss <zev@bewilderbeest.net>
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/platform_device.h>
> +#include <linux/regulator/consumer.h>
> +
> +struct efuse {
> +	struct regulator *reg;
> +	struct {
> +		unsigned int cache;
> +		unsigned long ttl;
> +		unsigned long fetch_time;
> +		struct mutex lock;
> +	} error_flags;
> +};
> +
> +/* Ensure that the next error_flags access fetches them from the device */
> +static void efuse_invalidate_error_flags(struct efuse *efuse)
> +{
> +	mutex_lock(&efuse->error_flags.lock);
> +	efuse->error_flags.fetch_time = 0;
> +	mutex_unlock(&efuse->error_flags.lock);
> +}
> +
> +static ssize_t efuse_show_operstate(struct device *dev, struct device_attribute *attr,
> +				    char *buf)
> +{
> +	struct efuse *efuse = dev_get_drvdata(dev);
> +	int status = regulator_is_enabled(efuse->reg);
> +
> +	if (status < 0)
> +		return status;
> +
> +	return sysfs_emit(buf, "%s\n", status ? "on" : "off");
> +}
> +
> +static ssize_t efuse_set_operstate(struct device *dev, struct device_attribute *attr,
> +				   const char *buf, size_t count)
> +{
> +	int status, wantstate;
> +	struct efuse *efuse = dev_get_drvdata(dev);
> +	struct regulator *reg = efuse->reg;
> +
> +	if (sysfs_streq(buf, "on"))
> +		wantstate = 1;
> +	else if (sysfs_streq(buf, "off"))
> +		wantstate = 0;
> +	else
> +		return -EINVAL;
> +
> +	status = regulator_is_enabled(reg);
> +
> +	/*
> +	 * We need to ensure our enable/disable calls don't get imbalanced, so
> +	 * bail if we can't determine the current state.
> +	 */
> +	if (status < 0)
> +		return status;
> +
> +	/* Return early if we're already in the desired state */
> +	if (!!status == wantstate)
> +		return count;
> +
> +	if (wantstate)
> +		status = regulator_enable(reg);
> +	else
> +		status = regulator_disable(reg);
> +
> +	/*
> +	 * Toggling operstate can reset latched status flags, so invalidate
> +	 * the cached value.
> +	 */
> +	efuse_invalidate_error_flags(efuse);
> +
> +	if (!status && regulator_is_enabled(reg) != wantstate) {
> +		/*
> +		 * We could do
> +		 *
> +		 *   if (!wantstate)
> +		 *     regulator_force_disable(reg);
> +		 *
> +		 * here, but it's likely to leave it such that it can't then
> +		 * be re-enabled, so we'll just report the error and leave it
> +		 * as it is (and hopefully as long as our enable/disable calls
> +		 * remain balanced and nobody registers another consumer for
> +		 * the same supply we won't end up in this situation anyway).
> +		 */
> +		dev_err(dev, "regulator_%sable() didn't take effect\n", wantstate ? "en" : "dis");
> +		status = -EIO;
> +	}
> +
> +	return status ? : count;
> +}
> +
> +static int efuse_update_error_flags(struct efuse *efuse)
> +{
> +	int status = 0;
> +	unsigned long cache_expiry;
> +
> +	mutex_lock(&efuse->error_flags.lock);
> +
> +	cache_expiry = efuse->error_flags.fetch_time + efuse->error_flags.ttl;
> +
> +	if (!efuse->error_flags.ttl || !efuse->error_flags.fetch_time ||
> +	    time_after(jiffies, cache_expiry)) {
> +		status = regulator_get_error_flags(efuse->reg, &efuse->error_flags.cache);
> +		if (!status)
> +			efuse->error_flags.fetch_time = jiffies;
> +	}
> +
> +	mutex_unlock(&efuse->error_flags.lock);
> +
> +	return status;
> +}
> +
> +static DEVICE_ATTR(operstate, 0644, efuse_show_operstate, efuse_set_operstate);
> +
> +#define EFUSE_ERROR_ATTR(name, bit)							    \
> +	static ssize_t efuse_show_##name(struct device *dev, struct device_attribute *attr, \
> +					 char *buf)                                         \
> +	{                                                                                   \
> +		struct efuse *efuse = dev_get_drvdata(dev);                                 \
> +		int status = efuse_update_error_flags(efuse);                               \
> +		if (status)                                                                 \
> +			return status;                                                      \
> +		return sysfs_emit(buf, "%d\n", !!(efuse->error_flags.cache & bit));         \
> +	}                                                                                   \
> +	static DEVICE_ATTR(name, 0444, efuse_show_##name, NULL)
> +
> +EFUSE_ERROR_ATTR(under_voltage, REGULATOR_ERROR_UNDER_VOLTAGE);
> +EFUSE_ERROR_ATTR(over_current, REGULATOR_ERROR_OVER_CURRENT);
> +EFUSE_ERROR_ATTR(regulation_out, REGULATOR_ERROR_REGULATION_OUT);
> +EFUSE_ERROR_ATTR(fail, REGULATOR_ERROR_FAIL);
> +EFUSE_ERROR_ATTR(over_temp, REGULATOR_ERROR_OVER_TEMP);
> +EFUSE_ERROR_ATTR(under_voltage_warn, REGULATOR_ERROR_UNDER_VOLTAGE_WARN);
> +EFUSE_ERROR_ATTR(over_current_warn, REGULATOR_ERROR_OVER_CURRENT_WARN);
> +EFUSE_ERROR_ATTR(over_voltage_warn, REGULATOR_ERROR_OVER_VOLTAGE_WARN);
> +EFUSE_ERROR_ATTR(over_temp_warn, REGULATOR_ERROR_OVER_TEMP_WARN);
> +
> +static struct attribute *attributes[] = {
> +	&dev_attr_operstate.attr,
> +	&dev_attr_under_voltage.attr,
> +	&dev_attr_over_current.attr,
> +	&dev_attr_regulation_out.attr,
> +	&dev_attr_fail.attr,
> +	&dev_attr_over_temp.attr,
> +	&dev_attr_under_voltage_warn.attr,
> +	&dev_attr_over_current_warn.attr,
> +	&dev_attr_over_voltage_warn.attr,
> +	&dev_attr_over_temp_warn.attr,
> +	NULL,
> +};
> +
> +static const struct attribute_group attr_group = {
> +	.attrs = attributes,
> +};

ATTRIBUTE_GROUPS()?

> +
> +static int efuse_probe(struct platform_device *pdev)
> +{
> +	int status;
> +	struct regulator *reg;
> +	struct efuse *efuse;
> +	u32 cache_ttl_ms;
> +
> +	reg = devm_regulator_get(&pdev->dev, "vout");
> +	if (IS_ERR(reg))
> +		return PTR_ERR(reg);
> +
> +	status = regulator_enable(reg);
> +	if (status) {
> +		dev_err(&pdev->dev, "failed to enable regulator\n");
> +		return status;
> +	}
> +
> +	efuse = devm_kzalloc(&pdev->dev, sizeof(*efuse), GFP_KERNEL);
> +	if (!efuse)
> +		return -ENOMEM;
> +
> +	efuse->reg = reg;
> +	mutex_init(&efuse->error_flags.lock);
> +
> +	if (!of_property_read_u32(pdev->dev.of_node, "error-flags-cache-ttl-ms", &cache_ttl_ms))
> +		efuse->error_flags.ttl = msecs_to_jiffies(cache_ttl_ms);
> +
> +	platform_set_drvdata(pdev, efuse);
> +
> +	return sysfs_create_group(&pdev->dev.kobj, &attr_group);

You just raced with userspace and lost :(

Set the default groups for your platform driver and then the driver core
will automatically create/remove them for you, no need for you to do
anything directly with them at all.

thanks,

greg k-h